A three-year epidemiologic study is proposed to evaluate the respective roles of, and possible interactions between, physical activity and dietary habits in the etiology of adenocarcinoma of the colon. Specifically, the study is designed to test the hypotheses that (a) physical inactivity increases the risk of colon cancer, especially cancers of the left side of the colon, and (b) physical inactivity acts as an effect modifier or as a confounding factor in the relation between dietary factors and colon cancer risk. Dietary habits to be examined include usual past frequency of consumption of (a) fats--total, saturated and polyunsaturated--, (b) beef and all meats, (c) milk and other dairy products, (d) dietary fiber, (e) cruciferous vegetables, and (f) vitamins A, C, ande E. The case-control method will be used. Cases will be all newly diagnosed, eligible cases of adenocarcinoma of the colon identified in residents of Los Angeles County by the Los Angeles County/USC Cancer Surveillance Program during the study period, until 750 cases have been enrolled. Study subjects will be white men and women who speak English and are between the ages of 45 and 69. Controls will be age-, sex-, and raae-matched persons chosen from the neighborhood of the cases using a 1:1 matching design. Data will be obtained by personal interviews in the respondents' home by trained interviewers using a structured, precoded questionnaire. The questionnaire will attempt to assess lifetime physical activity levels (both at work and at leisure) but will emphasize the 30 years prior to the diagnosis of the case. It will also elicit information about specific dietary habits (food frequencies), medical history, and use of drugs (e.g. laxatives, vitamin supplements, etc.). The diet section of the questionnaire will be developed and analysed by the UCLA Diet and Cancer Epidemiology Unit by means of a subcontract to the UCLA School of Public Health.